Avoids permanent break of resolv.conf.

The resolv.conf file gets updated by resolvconf, maintaining it as a
symlink allows the system to reset it during boot time. That is useful
when the app has a hard crash that gives no chance to roll back our
changes.

[Closes #4633]
Merge remote-tracking branch 'refs/remotes/ivan/bug/4633-fix-resolvconf-usage' into develop